Microwave diathermy has been widely used in many fields such as in the metallurgical industry, food production, medical treatment, etc. Recently, in the medical field various microwave diathermy apparatus for treating diseases, in particular, cancers, have been developed to eliminate side effects caused by radioactive and chemical therapies, and to make these therapies more effective. Microwave diathermy can be used to make polar molecules in active tissues rotate at high speeds in the microwave electromagnetic field, resulting in the generation of heat which causes the temperature of the lossy medium in the electromagnetic field to rise considerably. At such temperatures, cancer cells in a diathermical region can be killed or their vitality reduced.
An example of a microwave diathermy apparatus is the BSD-400 mobile hyperthermia system manufactured by BSD Medical Corporation of the United States of America, which a sticking-contact type of microwave diathermy apparatus comprising a microwave source with a maximum output power of 400 watts and an output frequency of 915 MHz; a circular microwave radiator with an output port used to stick on the body surface of a cancer patient for microwave-diathermizing deeply over the position of the cancer into the body of the cancer patient; an optical fiber temperature-measuring system for measuring the temperature at the position of diathermizing on the patient; and a computer based control and display system for displaying a temperature value measured by the optical fiber temperature-measuring system and for controlling and regulating the output power of the microwave source and consequently regulating the temperature at the microwave-diathermizing position to obtain the optimum therapeutic benefit in response to the temperature signal from the optical fiber temperature-measuring system. The microwave output power from the sticking-contact type of microwave-diathermy apparatus attenuates hyperbolically, as the depth of diathermy of the medium increases. In other words, the microwave power density at the output port sharply attenuates and the characteristic curve of power density-to-distance is very steep. Therefore, at the diathermized position, the temperature of the patient's body surface is higher than that under the surface, and this may easily cause the patent's skin to burn. Such a diathermy apparatus has an effective diathermic depth of 3-4 cm only, which is curative in respect of shallow tumors only, but not curative in respect of deep tumors.
In order to overcome the defects of this prior art apparatus and to increase diathermical depth, some other methods and apparatus have been developed, for example: RF-8 diathermy apparatus (Japan) with a frequency of 8 MHz, and BSD-2000 diathermy apparatus (USA) with a frequency range from 60 to 120 MHz, when a patient is treated by either of the above apparatus, the subcutaneous fat at the heated position can be easily overheated and the skin at the heated position must be cooled by water bags. Further more, since it is difficult to focus an RF electro-magnetic wave on a particular point, a large area of lossy medium has to be RF-heated, when patients are treated for chest cancer or upper-abdominal cancer, they may go into shock. Furthermore, the temperature at deeper parts of the body is not high enough, resulting in a poor curative effect.
An intracavitary diathermy method can also be used to diathermize a deep part of a lossy medium by inserting a small-sized microwave radiator into deep cavites such as the vagina, rectum, esophagus, or nasal cavity. However, only a small area can be diathermized using such a method and the internal surfaces of the cavity, might be burnt. This method can not be used in the treatment of such deep cancers as liver cancer, lung cancer and stomach cancer.
An inter-tissue diathermy method can be also used to directly heat a tumor by surgically implanting a microwave antenna or a RF electrode into the tumor. This method results in an uneven temprature distribution in the heated tumor and after a diathermical treatment the implanted microwave antenna or the RF electrode must be surgically removed. Therefore, when multiple treatments are needed this method can not be used because frequent operations have to be performed to implant and remove the antenna or electrode.